1. Field of the Invention
Embodiments of the invention generally relate to an apparatus for heating large area substrates in a processing system.
2. Background of the Related Art
In the fabrication of flat panel displays, transistors and liquid crystal cells, metal interconnects and other features are formed by depositing and removing multiple layers of conducting, semiconducting and dielectric materials from a glass substrate. Processing techniques include plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), etching, and the like. Plasma processing is particularly well suited for the production of flat panel displays because of the relatively lower processing temperatures required to deposit film on glass substrates and good film quality which results from plasma processes.
An exemplary type of flat panel display film is amorphous silicon (α-Si), which is used for PDA's, cell phone displays, monitors, big screen televisions, and the like. A heat treatment step is required in amorphous silicon film processing to remove moisture from the glass substrate after deposition. For example, a heat treatment step for amorphous silicon film includes heating the film disposed on the glass substrate to a temperature of up to about 400 degrees Celsius. Thus, cluster tools configured to process glass substrates may include heat treatment chambers to enhance the properties of deposited films.
Typically, heat treatment chambers thermally process one or more substrates through a combination of gas convection and heat radiation. Unfortunately, as the chamber walls and other internal chamber components provide conduction paths within the chamber, temperature control is difficult due to heat losses and gas convection currents within the heat treatment chamber. This combination of heat losses and convection currents creates a constantly fluctuating substrate-heating environment that prevents uniform heating of the substrate. Additionally, as the size of glass substrate is increased, the heat loss and convection current effects on substrate heating uniformity become more pronounced, which results in non-uniform temperature across the width of a single glass substrate, along with substrate to substrate variation, which impedes process repeatability.
Moreover, heat treatment chambers are often very big to accommodate the long edges of the large area substrate further exacerbating the heating issues by increasing the area and volume to be heated. For example, as the demand for larger computer displays, monitors, flat-screen televisions, and the like increases, the sizes of large area glass substrates upon which these devices are fabricated have increased from about 500×650 mm to about 1500×1800 mm over just a few years, and are envisioned as even larger. As these long substrate edges have faster rates of heat loss as compared to the center of the substrate, uniform heating of these increasingly larger area substrates is particularly difficult to achieve. Thus, traditional heat treatment chambers and heating processes do not provide acceptably uniform substrate heating for an efficient and cost effective heating process.
Therefore, there is a need for an improved apparatus for uniform heat processing of a plurality of substrates in a processing system.